Brake control device



Oct. 11, 1933.

B. S. AIKMAN BRAKE CONTROL DEVICE Filed Feb. 1'7, 1933 2 Sheets-Sheet 1 BUR INVENTOR TON SAIKMAN ATTORNEY Oct 11, 1938.

B. S. AIKMAN BRAKE CONTROL'DEVICE Filed Feb. 1?,"1938 2 Sheets-Sheet 2 ATTORNEY Patented Oct. 11, 1938 UNITED STATES PATENT OFFICE 19 Claims. (Cl. soc-21 This invention relates to brake control devices and has particular relation to brake control devices including equipment forguarding against sliding of the wheels on vehicles such as railway cars.

As is well known, when the braking force with which brake shoes are applied to retard the ro-' tation of a vehicle wheel is sufliciently great to cause the coefficient of adhesion between the vehicle wheel and the road surface'or rail on which the wheel rolls to be exceeded; the vehicle wheel slips, that is, decelerates rapidly toward a locked-wheel state. As employed herein, the term slip or slipping" refers to rotation of a vehicle wheel at a speed less than "a speed corresponding to vehiclespeed and the time during which a wheel is slipping is referred to as the slipping time or slipping period. The term slide or sliding, as employed herein, refers to the dragging of a vehicle wheel along the rail in a locked-wheel state, as distinguished from the slipping of the wheel.

Various devices and mechanisms have been proposed which are responsive to the slipping of a vehicle wheel, for effecting a release of the brakes on the slipping wheel sufficiently rapidly to prevent the Vehicle wheeldecelerating to a locked-wheel state and thus'permitthe vehicle wheel to be restored to a speed of rotation'corresponding to the vehicle speed without sliding.

It is an object of my present invention to provide a novel arrangement for releasing the brakes on a vehicle wheel substantially instantaneously upon the slipping of the vehicle wheel and there' pressure or partial vacuum in a chamber upon the attainment of a predetermined differential in the rotative speeds of the vehicle wheels associated with the different axles, whereby the release of the brakes on the vehicle wheelsassociated with the axles is initiated.

The above objects, and other objectsof myinvention which will be made apparent hereine t are ai e by n ustrat ve, e bq m nt .greater detail, the brake cylinder l l contains the usual piston, not shown, which is shifted in response to the pressure of fluid supplied tothe of my invention subsequently to be described and shown in the accompanying drawings, wherein Fig. 1 is a diagrammatic view, with parts in section, showing the essential parts of a brake control equipment embodying my invention, and 5 Fig. 2 is a sectional view, taken on the line 2-2 of Fig. 1 showing in further detail the arrangement of parts and the construction of the equipment shown in Fig. 1.

Description of equipment 'unit IZ'of the type described in detail and claimed in' my copending application Serial No. 176,184, filed November 24, 1937, and assigned to the same assignee as is the present application. The equipment also includes a source of fluid under pressure, such as a main reservoir l3 and'a selflapping manually operative brake valve 14 of the 25 T pe described in detail and claimed in Patent 2,042,112 of Ewing K. Lynn and Rankin J. Bush.

According to my invention, the equipment further includes a pump and valve unit I5 associated with and operated by rotation of the axle of the rear wheels 1, and a pump unit It associated with and operated by rotation ofthe axle of the forward wheels 6 of the wheel truck.

Considering the parts of the equipment in inder piston is connectable with thespace on the opposite or usualnon-pressure side of the piston 4.5

' .underthecontrol of the valve unit l2, fluid un ,der. pressure flowing to the-non-pressure side of the brake cylinder piston as through a pipe I! connecting the flanges at opposite ends of the brake cylinder.

' In view of the complete description of valve unit given in mycopending application, mentioned above, only a brief description of the functions performed by the valve unit is deemed man anese.The-v e uni n m Q may be efiected in the conventional manner by a the operator of the vehicle.

Connecting the valve unit l2 and til-taunt valve unit I5 is a so-called trigger pipe lfl which is charged with fluid under pressure according to the pressure established in the supply pipe 18 while'the valve unit I2 is in its normal condition. Upon a sudden reduction of the pressure in trigger pipe IS, without reduction of themessure in supply pipe I8, the valve unit l2 is '01)- er 'a'ted to "first closethe communication from the supply pipe [8 to the usual pressureside er the brake cylinder piston and then to establish communication between the usual pressure and non-pressure sides of the "brake cylinder piston.

The fluid pressure on -the pressure slide of the brake cylinder piston is accordingly reduced to the pressure o f equalization with the pressure established on the non pre s sur e side of the brake cylinder pist n by flow offluid under pressure from the pre ure side to the non-pressure side of the brake cylinder piston When the'fluid sure on the opposite sides of the bra e cylinder piston thus becomes "substantially equalized, the usual release spring," not shown, and associated with the brake cylinder piston, returns the piston to its release 'position and the brakes on the wheels Band 1 are thus released] When fluid pressure is again restoreenl trigger pipe 19, valve unit l'2 perates close the connnunica'tion between the pressure and ndn':

' pressure, sides of the brake cylinder piston rid we Qne an e h ust. eefifi u roueh w i h h ffl i fl fi re Q t e alf eipressure side of the brake "cylinder piston is vented, reapplication of the and 7 being thus effected.

Valve unit I2 is not responsive 'to restoration of fluid pressure in trigger pipe l9, however, to frestore. the communication between the supp y pipeluand the pressure side of the brake glinder piston. Consequntl'y, the reapplication "of the brakes efiectedby the release or" fluid under pressurefrorn the usual nee-pressure side of the brake cylinder piston is lii nited to adegree corresponding to the reduced pressure remaining on the usualpress'ure'side of the brake cylinder pis ton. Asa result, when the'sudden reduction of the pressure in the trigger; pipe I9 is initiated upon slipping of a .vehi'c'le wheel, as will be described hereinafter, the 'reapplic'ation of the brakes onthe vehicle wheels is limited to 'a de-' greedess than that wlriich "initiated the slipping e d; P il th P95 1 2 cii r' i of s p n of the vehicle wheels is substantially eliminated.

'A further operating'characteristic of the valve un h ha the n .S IflUi H d P' F sure from the usual non-pressure side of the brake cylinder piston is delayed to insure restoratha o a slip in remc ewhe b a p corresponding to vehicle speed before reapplicationfof the brakes becomes effective, thus additionally insuring against the recurrence of wheell rinew 'In view of the'ccmplete description of-theselfl brakes 1m wheels 15 tion thereof into an application zone to establisha pressure in the supply pipe I8 corresponding to the degree to which the operating handle is displaced out of its normal position. When the operating handle is in its normal release position, the supply pipe I8 is vented to atmosphere at the brake valve and the supply of fluid under pressure from the reservoir 53 is cut off.

As seen more clearly in 2, the pump and valve unit 15 comprises a casing which is bolted 'or otherwise suitably secured to the external face of the journal 23 a'tthe outside end of the axle 24 of the wheel 1 on which is suitably sup-ported and guides a truck side frame member 25- of conventional construction.

The casing of the pump and valve unit 15 has formed therein in coaxial relation to the axle 24 a bore 21 in which the outer end of the axle 24 is partiallz. receive-d. Secured to the outer end of the axle 2'4 and properly centered as by a 'cente'rin'g projection is an adapter disk 28 which may be secured to the axle 24 for rotation therewith by a plurality of pins 29.

Embodied in the casing of the pump and valve unit'lfi is a gear type pump comprising two coopcrating intermeshed gear wheels 3| 'and32. The shaft 33 of the gear wheel is suitably journaled inithe casing in coaxial alignment with the axle 24 and has a squared projection34 at one end which extends into a conforming recess 35 in the adapted'disk 28. Accordingly,the'gear wheel 31 of the is rotated 'at a speed and 'in the direction of rotation -of the wheel I and axle 24,

while the gear wheel 32 'of the pump is rotated in the oppositedirection.

The casing of the pump and valve unit 55 has formed thereiniat the lower portion thereof a storage chamber 31 for liquid such as oil, a supply of liquid being admitted to the storage cham- 1 be'r3'l through'afilling'opening'38. I A removable plug 39 provided for the'filling opening and has breather ports 41 therein for maintaining the pressure in the storage chamber Sl at atmospheric "pressure. an opening 44 through which the liquid in the chamber 3''! maybe drained, a suitable removable plug43 'for the opening 44' being provided. The portion of the casing for supporting the pump gear wheels is arranged to extend downwardly 1 cated by the arrowsin Fig. 1, the liquid which,

rises in the intake passage '45 to the height in the storage chamber 37 is withdrawn from the intake passage 45 and Lforced by the teeth of the gear whels3l main through the corresponding arouate grooves and delivered into the discharge chamber' ifi.

The pump l8, associated with the axle of the forward vehicle wheel 6, is similar in construction At the bottom of the casing is formed to provide an intake passage or chamber 48' and a discharge chamber and passage 49.

The discharge chamber 46 of the pump and valve unit [5 is connected to, the intakechamber 48 of the pump l 6 through a suitable flexible tube or pipe 5| and the discharge passage 49 of the pump I6 is connected by a suitable flexible tube or pipe 52 to a return passage 53in the casing of the'pump valve unit l5 which opens upwardly into the intake passage 45.

A suitable supporting and protecting'sleeve element 54 is provided for the flexible pipes. 5| and 52, the sleeve being secured; as by brackets 55, to the side frame of the vehicle wheel truck;

7 It will thus be seen that the liquid discharged into the discharge chamber 46 of the pump and valveunit l5 flows through the pipe 5| to the intake chamber 48 of the pump l6 which, in turn, returns it through the pipe 52 to the intake passage 45 of the pump and valve unit l5. If the forward and rear vehicle wheels 6 and 1 are rotating at the same speed, the pump [6 returns If the forward vehicle wheel 6 rotates at a speed less than the speed of rotation of the rear vehicle wheel 1; the pump of the pump and valve unit l5 delivers-liquid to the pump l6 faster than the pump l6 can return it to the intake passage 45 and, consequently, the liquid pressure in the discharge chamber 46 of the pump andvalve unit [5 is increased above the normal pressure therein.

In a similar manner, if the rearvehicle wheel 1 rotates at a speed less than the rotative speed of the forward wheel 6, the pump of the pump and valve unit l5 cannot deliver liquid to the pump l6 as rapidly as it is discharged or returned by the pump I6 to the intake passage 45land, conse- 'quently, a partial vacuum is produced in the discharge chamber 46 of the pump and valve unit l5. The trigger pipe l9 opens into a passage 51 in the casing of the pump and valve unit l5 and valve mechanism, presently to be described, is.

provided for opening the passage 51 to atmosphere'and thus effecting a sudden reduction of the pressure in the triggerpipe l9 upon a predetermined increase of pressure in the discharge chamber 46 or upon the creation of a predetermined partial vacuum in the discharge chamber 46.

. For reducing the pressure in the'trigger pipe l9 upon the production of a partial vacuum in the discharge chamber 46 of thepump and valve unit l5, a piston valve 59 operativein a suitable bore 69 in the casing of the pump and valve unit I5 is provided.' The piston valve 59 has formed thereon a pin valve 6| which is urged into seated relation on an associated valve seat, formed on the.

casing, by a coil spring 62 interposed between the piston valve 59 and 9. lug- 63 adjacent the end'of the bore 66 in which the piston valve 59 "operates. The space surrounding the pin'valve'Hat the outer seated area thereof is constantly open to atmosphere through a vent port 65and the pin valve 6| is thus ada'pted to control the exhaust of fluid under pressure from the passage 51 through'the port 65. The face of the piston valve 59 on whichthe spring 62 acts is open to the discharge chamber 46 and thus upon the production of a partialvacuum in the discharge chamber 46, the atmospheric pressure acting on the outer seated area of the piston valve is effective to overcome the force of the spring 62 and unseat the pin valve 6| fromits associated valve seat to cause fluid under pressure in the passage-51 to be vented suddenly to atmosphere through the exhaust port 65.

Fluid" under pressure is also suddenly released from the passage 51 upon an increase in the pressure of the liquid pressure in the discharge on the other side to the liquid pressure in the discharge chamber 46. When the pressure on opposite sides of the piston 61 is substantially equal, it is urged in the right-hand direction into engagement with a stop lug 1| formed on the casingwithin the discharge chamber 46 by a coil spring 12 interposed between the casing and the piston. q

r The poppet valve 68 is'contained in the passage 51 and is normally urged into seated relation on an associated valve seat by a coil spring 13. The poppet valve 68 has a fluted stem 14 which is guidably supported in a' suitable bore in, the casing and which engages at the end thereof a stem 15 formed on the piston 61. The casing of the pump and valve unit I5 is formed so that the flutedstemjg" of, the valve is open'to atmosphere-along a portion thereof;

The length of the'flutedstem 14 of the valve 68 and stem 15 of the piston 61 is such that when the piston 61 is urged in the right-hand direction into contact with the stop lug 1|, the poppet valve 68 is seated. Uponan increase of the liquid pressure in the discharge chamber 46 sufficient to overcome the force of the spring 12, the piston 61 shifts inv the left-hand direction and thus unseatsthe poppet valve 68.

With valve 68 unseated, fluid under pressure is exhausted from the passage 51 and the connected triggerpipe 9 to atmosphere.

' In order to prevent the development of excessive liquid pressure in the discharge chamber 46 of the pump and valve unit [5, a loaded check valve" is provided. The check valve 18 is illustrated asof the ball type and is loaded as by means of a coil spring which urges the ball check valve into seated relation on an associated valve seat to close communication be-' tween the discharge chamber 46 and the return passage 53 through a passage 8 I When the pressure developediinthe discharge chamber 46 .overcomes the force of the spring 19, the ball check valve .18 is unseated and the liquid pressure is thus relievedby flow of liquid through the passage M 'to the return passage 53 which, being in communication with the-storage chamber 31, is at atmospheric pressure. f j The vehicle wheels 6 and 1 are as a practical matter', not-always of identically-the same diam quently, a partial vacuum or an increase of liquid pressure may be developed normally in the discharge chamber 46 of the pump and valve unit l5 due to the difference in operating speeds of the two pumps. In order to prevent undesired reduction of the pressure in the trigger pipe 19, under the circumstances just described, a bypass communication is provided between the discharge chamber 46 and the storage chamber 31 which prevents substantial variation from atmospheric-pressurein the discharge chamber 46 unless the rotative speeds of the two vehicle wheels 6 and 1 differ by a substantial amount which would occur only in the event that either one of the wheels slips with respect to the other.

This communication is established by means of a passage 83 in the casing which is connected by a tube 84 to the discharge chamber 46 and by a tube 85 to the storage chamber 31. The tube 84 extends upwardly, terminating adjacent the uppermost part of the discharge chamber 46,

and has a restricted port 86 at theupper end thereof, The tube 85 extends downwardly and is open at the lower end thereof adjacent the bottom of the storage chamber 31. The port 86 in the tube 84 is of sufficient size that liquid may flow therethrough from the discharge chamber 46 to the storage chamber 31 or from the storage chamber 31 to the discharge chamber 46 .rapidly enough to prevent any substantial increase in the pressure or production of a partial vacuum in the discharge chamber 46 such as might be caused by the slight difierence in diameters of Vehicle wheels 6 and. I. When the difference in the rotative speeds of the two wheels 6 and 1 is greater than that due merely to the diil'erence in diameters thereof, such as results from the slipping of one wheel with respect to thevother,

I the port 86 so restricts the flow of liquid between the discharge chamber 46 and the storage chamber 31 as not to prevent the increase of liquid pressure in the discharge chamber or the production of a partial vacuum therein.

The communication between discharge chamber 46 and the storage chamber 31 through the passage 83 and tubes 84 and 85 serves the additional purpose of releasing air trapped in the upper portion of the discharge chamber 46 to atmosphere. It will be apparent that when the pump of the pump and valve unit I5 is initially operated and liquid is deliveredto the discharge chamber 46, air is trapped in the discharge chamber 46 above the level of the liquid delivered into the chamber. Such trapped air'may interfere with the proper operation of the piston valve 59 and of poppet valve 68 and is accordingly objectionable. It will be apparent that by causing the tube 84 to terminate at the uppermost portion of the discharge chamber 46, the

slightest amount of air trapped in the discharge chamber may be released by flow through the tube 84, passage 83 andtube 85 to the storage chamber '31 where it may bubble upwardly through the'liquid and discharge to atmosphere through the restricted breather ports 4| in the plug 39 secured in the filling opening 38.

Operation of equipment Let -it.be assumed "that the mainireservoirI3 ischarged to the normal pressure carried therein, as from a fluid compressor not shown, that the brake .Valve handle 21 is in its .normal re lease-position, that a supply of liquid is 'contained in the stora e chamber 31 of the pump and valve'unit l5 and that the vehicle is traveling along the road or track under power or coasting. With the brake valve handle 2! in its release position, the supply pipe I8 is vented to atmosphere and consequently fluid under pressure is released from the pressure side of the brake cylinder piston and the brakes are released.

If it is desired to eiTect an application of the brakes on the vehicle wheel 6 and l, the operator first shuts oif the power if the power is on andthen shifts the brake valve handle 2| from its release position into the application zone to a desired degree. Accordingly, the self-lapping brake valve device I4 operates to supply fluid under pressure from the main reservoir l3 to the supply pipe land by way of the valve unit l2 tothe pressure side of the brake cylinder piston thereby effecting an application of the brakes to a degree corresponding to the displacement of the brake valve handle out of its release position.

Aslong as the vehicle Wheels 6 and "I continue to rotate at speeds corresponding to vehicle speed, the valve, unit I2 is conditioned to establish communication between thesupply pipe l8 and the pressure side of the brake cylinder piston and. thus the degree of application of the brakes will be maintained unless the operator varies thedegree ofdisplacement of the brake valve handle 24 from its release position either to increase the degree or decreasethe degree of the application.

If the degree of the application is such, or if the condition of the road surface or track rails is such, that the forward wheel .6 in the vehicle truck begins to slip, the resultant increase in the liquid pressure in the discharge chamber 46 of the pump and valve unit i5 causes unseating of thepoppet valve 68 and the consequent reduction of pressure in the trigger pipe 99. As a result, the valve unit. I2 is operated to cut off the further supply of fluid under" pressure from the supply pipe I8 and to establish communication through which the pressure on the usual pressure side of thebrake cylinder piston is equalized to the space in the brake cylinder on the usual'nonpressure side of the brake cylinder piston. This equalization of pressure on opposite sides of the brake cylinder piston occurs so rapidly that the brakes on the vehicle wheels 6 and l are released substantially completely before the vehicle wheel 6 attains the locked-Wheel state. Accordingly, upon the release of the brakes the vehicle wheel 6 begins to accelerate back toward under pressure from the usual non-pressure side of the brake cylinder pistonv without reopening the communication through which fluid under pressure is supplied from the supply pipe l8 to the pressure side of the brake cylinder piston. Thus,-,the brakes are reapplied on the vehicle wheels 6andl at a reduced degree corresponding to the reduced pressure maintained on the usual pressure side of the brake cylinder piston. Accordingly, as previously indicated, due both to 21? .the delay in efiecting reapplication of the brakes :is again vented to atmosphere as previously de scribed and the valve unit I2 again operates to equalize the fluid pressure on the usual pressure side of the brake cylinder piston into the space on the usual non-pressure side of the brake cylinder piston and thus again effects release'fof the brakes. I

When, due to the release of thebrakes, the

vehicle wheel 6 again returns to a speed corre-' sponding substantially to vehicle speed and the valve unit l2 operates to release fluid under pressure from the usualnon-pressure side of the brake cylinder piston to effect reapplication of the brakes, the degree of the application is further reduced from that which initiated the slipping of the wheel to a degree corresponding to the pressure remaining on the pressure side of'the brake cylinder piston. v c

In the event that the vehicle wheel 1 begins to slip with respect to the vehicle wheel 6 during an application of the brakes, a partial vacuum is produced in the discharge chamber 46 as pre-' viously explained and, as a result, the pin valve 6! on the piston valve 59 is unseated and the trigger pipe i9 is similarly vented to atmosphere through the exhaust port.65. The valveunit I2 is thus first operated to effect the release of the brakes before the vehicle wheel I can attain the.

locked-wheel state an'dthen, upon the return of the vehicle wheel I to a speed'corresponding'sub stantially to vehicle speed, tov effect the reapplication of the brakes to a reduced degree. Obviously, when'the' vehicle wheel 1 returns to a speed correspondingto vehicle speed duefto the release of the brakes, the pressure in the discharge chamber 46 of the pump and valve'unit I5 is again increased to substantially atmospheric pressure and consequently the spring 62 reseats the pin valve 6! on the piston valve 59 so that the trigger pipe l9, may again be recharged.

When the vehicle comes to a stop and the operator desires to release the brakes prior to again starting the vehicle, he merely shifts the brake valve handle 2! to release position. In such case, the supply pipe I8 is vented to atmosphere and the valve unit l2 operated to reopen communication between the pressure side of the brake cyliinder piston and the supply pipe l8 so thatfluid under pressure acting on the pressure 'sideof the brake cylinder'piston is released to atmosphere at the brake valve [4.

Summary line between one pump and the other is maintained substantially at atmospheric pressure.

When one of the forward wheels or one ofthe rear wheels of the vehicle truck slips with respect "exit, is:

to the other, an increase of pressure or a partial 'vacuum is produced, in the chamber which is .efiective through suitable responsive valve devices to produce a release of the brakes on the vehicle wheels 'su'filciently rapidly'to prevent the slipping wheelsiirom attaining the locked-wheel state.

When the slipping wheel returns to a speed corresponding substantially tojvehicle speed, the

restoration of the normal atmospheric pressure in the chamber causes reapplication of the brakesclaim as new and desire to secure by Letters Pat- 1. A vehicle brake equipment comprising means for causing application of'theibrakes, means for causing release of the brakes while the firstsaid means is conditioned to cause application of the brakes, a chamber having fluid therein normally at a certain pressure, and means responsive to a certain increase or a certain decrease of fluid pressure in the said chamber with respect to said certain normal pressure for causing operation of the brake releasing means to release the brakes 2. A vehicle brake equipment comprising means operative to effect application and release of the brakes, means operative while the first said means for causing release and reapplication of the brakes, means providing a chamber having fluid V therein normally at a certain pressure, and means responsive to a certain increase or to a certain decrease in pressure with respect to saidcertain lease and reapplication means to effect reapplication of the brakes.

3. A vehicle brake equipment comprising means operative to cause application and release of the brakes, means for causing release of the brakes while the first said means is conditioned to'cause application of the brakes, means providing a chamber having fluid therein normally at atmospheric pressure and means responsive to a certain increase in pressure or tea certain decrease V in pressure with respect to atmospheric pressure in said chamber for causing operation of the brakereleasing means to release the brakes.

4. A vehicle brake equipment comprising means operativeto efiect application and release of the .is conditioned to'cause application of the brakes brakes, means efiective while the first said means is conditioned tocause application'of the brakes for causing release; and reapplication of the brakes, means providing a chamber having fluid therein normally at atmospheric pressure, and means responsive to a predetermined increase or decrease in pressure with respect to atmospheric pressure in said chamber for causing operation of the release and reapplication means to efiect release of the brakes and responsive to the return of atmospheric pressure in said chamber for causing the release and'reapplication means to effect reapplicationof the brakes.

5. A vehicle brake equipment comprising means for causing application of'the brakes, means ior at a certain pressure, means responsive to a certaininc'rease or a certain decreasebf pressure with respectto said certain pressure in said chamher for causing operation of the brake releasing "means to release the brakes; and means respon (sive to'a certain differential of speed of one vel0,

hiclewheel over a second vehicle wheel for effecting an increase of, pressure in said chamber and tea certain differential of speed 'of the second vehicle wheel over the said one vehicle wheel for effecting a reduction of pressure in said chamber with respect to'said certain pressure.

6. A vehicle brake equipment comprising means operative to effect application and release of the brakes, means operative while the first said means is conditioned to causeapplic'at'ron of the brakes for causing release "and reapplication of the brakes, means providing a chamber havingfluid her n n r a ly at a cert inp e su a' responsive :to a' certainincrease or to a certain decrease inv pressure with respect said certain pressure in said chamber for causing said release and reapplication means to effect release or the brakes and responsive to the returno'f said certain pressure of said "chamber forcausing said release and reapplication means to effect reapplication "of the'brakes, and means responsive to a pertain differential of speed fof one 'vehicl ewvheel "over a second vehicle wheel for effecting "increase in pressure in said chamber with respect to said certain pressure and to a certain differential of speed of the said second vehicle wheel over the said one vehicle wheel for effecting a reduction of pressure with respect tosaid certain pressure. I I r Y LA brake equipment for a"vehi'cie having "at least two separately rotatable wheels, means for e fecting an application of brakes on said wheels, means for effecting the release of the brakes from said wheels while the first said means is conditioned to effect applicatien'thereof, means providing a passage for fluid,:twopumps-sofarranged that "one pump delivers fluid; into said passage and the ether withdraws flu'id therefrom, one of said pumps being operated according to the rotative speed ofpne -of said wheels and the other of said pump being operated according 'to the rotative speed of the otherof said wheels so that the fluid pressure; in said passage depends upon the relative speeds at which the two pumps are operated, and means controlled according to the fluid pressure inz-said passage for 'c'ontrolling'said brake releasing means. i J 8. A vehicle brake equipment comprising means for effecting application of the, brakes, means for effecting release of the brakes while -the said means is conditioned to effect application of the brakes, a fluid circulatory system including two pumps operative respectively according toet'he rotative speeds of :two different vehicle wheels, and means responsive to variations of pressure in the system due to operation ofthe two pumps at different speeds forcontroll'ing the brake "releasing means.

9. A vehicle brake equipment "comprising means for effecting application of the brakes, means for effecting release an'dreapplication of the brakes while the first said ED162115 is conditioned to effect applicaitien of the brakes, a fluid circulatory system including two pumps operative respectively according to the rotative speeds of two different vehicle wheels, the pressurein a cerwagers taln portion of said system being mormally substantially at atmospheric 'pressure' as long as the two pumps operate at substantiallythe samespeed and increasing or decreasing with respect to atmospheric pressure when one of the pumps is operated at a speed different from the other, and means responsive to variations of the pressure in said portion of the system'above or below atmospheric pressure for causing operation of the release and reapplication means to effect release of the brakes and responsive to the restoration of atmospheric pressure in said portion of the system for causing operation of the release and reapplication means to effect reapplication of the brakes. I

10. A vehicle brake equipment comprising means fer efiecting application of the brakes, means f6!- efiecting release of the brakes while the first said means is conditioned to effect applicationof the brakes, a fluid circulatory system including two pumps operative respectively according to the rotative speeds of two different vehicle wheels, means responsive to variations of pressure in a certain portion of the system due to operation of the two pumps at different speeds for controlling the brake releasing means, and means for preventing a substantial variation from the normal pressure carried in the said certain portion of the circulatory system as long as the difference in the speed of operation of the two pumps does not exceed a certain amount of speed. 11. A vehicle brake equipment comprising means for effecting application of the brakes,

means for effecting release of the brakes while I the first said means is conditioned to effect application of the brakes, a fluid circulatory system including two pumps operative respectively ac cording to the rotative speeds of two different vehicle wheels, means responsive to variations of pressure-in said system due to operation of the two pumps at diiferentspeeds for controlling the brake releasing means? and means for'limiting the increase of; pressure in said system to a certain uniform pressure.

12. A vehicle brake equipment comprising means for effecting application of the brakes, means for eifecting release of the brakes while the first said means is conditioned to effect application of the brakes, a fluid circulatory ystem including two pumps operative respectively accordin to the rotative speeds of two different vehicle wheels, said pumps being efiective to main tain a certain normal pressure in said system as long as they operate at'substantially the same speeds and effective to cause an increase or a decrease in pressure with respect to the normal pressure when one of the pumps operates faster than the other, means responsive to a predetermined increase of the pressure in said system above the normal pressure for effecting operation 'ofthe brake reIeasing means to effect release of the brakes, and means responsive to a predetermined decrease of pressure in said system below the normal pressure carried therein to also cause said brake releasing means to eifect release of the to the intake passage of the other, said pumps being effective when operated at substantially the same speeds for maintaining a substantially unvarying'normal pressure in a portion of the system between the discharge of the said onepump 7 and the intake of the said other pump, effective when the said one pump operates at a higher speed than the said other pump to effect an increase of pressure in-the said portion of circulatory system, and effective when the said one pump operates at a slower speed from the said other pump to produce a partial vacuum in the said portion of the circulatory system, and means responsive to a predetermined pressure or to a predetermined partial vacuum in the said portion of the circulatory system for causing operationof the brake releasing means to effectrelease of the brakes.

14. A vehicle brake equipment comprising a brake cylinder having therein a .piston and two chambers located respectively on opposite sides of the piston, means for causing fluid under pressure to be supplied to one of said chambers to cause movement of the piston to effect applica-f tion of the brakes, valve means operative to connect said two chambers to equalize the fluid pressure on opposite sides of the piston and thereby effect release of the brakes, and means responsive to a certain differential in the rotative speeds of two different vehicle wheels for causing operation of the valve means. i

15. A vehicle brake equipment comprising a brake cylinder having therein a piston and two differential of rotative speeds of two different vehicle wheels to eflect operation of the valve means to establish communication between the two chambers.

'16. A vehicle brake equipment comprising a brake cylinder having therein a piston and two chambers located respectively on opposite sides of the piston, means for causing fluid under pres--,

sure to be supplied to one of said chambers to cause movement of the'piston to effect application of the brakes, valve means operative to establish communication between said two chambers to effect equalization of the fluid pressures on opposite sides of the piston and thereby efiectrelease of the brakes, a fluid circulatory system including two pumps operative respectively according to the rotative speeds of two different vehicle wheels, said pumps bein effective when operated at different speeds to effect an increase or decrease of the pressurein the circulatory system from a certain normal pressure carried therein, means responsive to a predetermined variation above or below the certain normal pressure in the circulatory system for effecting operation of said valve means.

17. A vehicle brake equipment comprising means for effecting application of the brakes, means for effecting release of the brakes while the first said means is positioned to effect application of the brakes, a chamber, two pumps operative respectively according to the rotative speeds of two separately rotatable vehicle wheels, said pumps being effective to cause an increase of pressure or a decrease of pressure-from a certain normal pressure in said chamber upon the occurrence of a difference in the rotative speeds of said two wheels, means responsive to a predetermined increase or a predetermined decrease from the normal pressure in said chamber for causing said brake releasing means to operate to effect release of the brakes, and means for preventing such predetermined increase or decrease from the normal pressure in said chamber unless the difference inthe'rotative speeds of said two wheels exceeds a certain amount.

, 18. A vehicle brake equipment comprising means for efiectingapplication of the brakes,

means for effecting release of the brakes while the first said means is conditioned to effect application of the brakes, two pumps operative respectively according to the rotative speeds of two separately rotatable vehicle wheels, means pro- 'viding two fluid passages between said pumps,

fluid being delivered from one of said pumps through one of said passages to the other of said pumps and from the other of said pumps through the other of said passages to the said one pump, said pumps being effective when the corresponding vehicle wheels are rotated at dif- .ferent speeds to cause an increase or a decrease in the normal pressure existing in said one passage, means responsive to a predetermined increase or to a predetermined decrease from the "normal pressure in' said one passage for causing operation of the said brake releasing means to effect release of the brakes, and means providing communication between said two passages for the flow of fluidin either direction therebetween to prevent substantial variation from the normal pressure in said one passage unless the difference between the rotative speeds of the two vehicle wheels exceeds a certain amount.

19. A. vehicle brake equipment comprising means for causing application of the brakes,

means operative to cause release of the brakes while the first said means is conditioned to cause application of the brakes, a chamber containing liquid normally at a certain pressure, means responsive to the occurrence of a differential between the rotative speed of one vehicle wheel and the rotative speedof a second vehicle wheel for effecting an increase of liquid pressure in said chamber, means responsive to a predetermined increase of liquid pressure in said chamber for causing operation of the brake release means to release the brakes, and means for releasing air BURTON S. AIKMAN. 

